Recently, a number of kinds of networks have been developed and implemented in a real life owing to the development of communication, computer and networking technology. A large-scaled network, such as wire or wireless Internet, which connects the whole world, exists while a small-scaled wire or wireless network exists, which connects digital devices in limited places such as general homes or companies. With the development of various types of networks, various interfacing techniques have been also developed, which connect networks or devices with each other to perform communication between them.
FIG. 1 illustrates an example of a wireless video area network (WVAN) which is a kind of a wireless private access network (WPAN). The WVAN is a network configured between digital devices within a limited place, such as home, within 10 m to ensure throughput of 4.5 Gbps or greater at a bandwidth of about 7 GHz, thereby supporting non-compression transmission of 1080 p A/V streams.
FIG. 2 illustrates an example of a structure of superframes used in the WVAN. Referring to FIG. 2, each superframe includes a beacon region to which a beacon is transmitted, a reserved region allocated to a random device by a coordinator in accordance with a request of devices, and an unreserved region where data are transmitted and received between the coordinator and a device or between devices in accordance with a contention based mode without being allocated by the coordinator, wherein each of the regions undergoes time division. The beacon includes timing allocation information in a corresponding superframe and management and control information of WVAN.
The reserved region is used to allow a device, to which a channel time is allocated by the coordinator in accordance with a channel time allocation request of the device, to transmit data to another device. Commands, data streams, asynchronous data, etc. can be transmitted through the reserved region. The unreserved region can be used to transmit control information, MAC command or asynchronous data between the coordinator and the device or between the devices. To avoid data collision between the devices in the unreserved region, a carrier sense multiple access (CSMA) mode or a slotted Aloha mode can be used. The length and the number of reserved regions and unreserved regions in each superframe may depend on superframe and may be controlled by the coordinator.
A specific device in the WVAN transmits a bandwidth request command to the coordinator so that the device can be allocated with channel resources for data transmission. The coordinator checks whether there are channel resources to be allocated to the device. If there are channel resources to be allocated to the device, the coordinator allocates the requested channel resources to the device. At this time, information of the channel resources allocated to the device, i.e., timing allocation information is forwarded to the devices within the WVAN through a beacon which will be transmitted later.
Accordingly, in order that a random device is allocated with channel resources by requesting the coordinator of the channel resources and transmits data by using the allocated channel resources, the device should wait for the time to receive at least next beacon. This method of allocating channel resources may have a problem when instant data transmission is required. In other words, if message exchange between two devices is instantly required, for example, if there is a previously set timing constraint to receive a response message to a message transmitted from a specific device to another device, a problem occurs in that the method of allocating channel resources according to the related art cannot fulfill the timing constraint. In this case, message exchange through a contention interval without allocation of channel resources may be considered. However, since the contention based message exchange may cause collision between devices, a problem occurs in that it is impossible to ensure certainty in message transmission and reception.